The coronary artery reactivity to acetylcholine and collagen was studied in rhesus macaques subjected to coronary angiography. Four experimental conditions were observed (a) control group; (b) macaques rendered hyperhomocyst(e)inemic resulting from a diet partially deficient in folic acid and choline; (c) macaques receiving an atherogenic diet; and (d) macaques receiving an atherogenic diet partially deficient in folic acid and choline. Our findings demonstrated that hyperhomocyst(e)inemia was associated with abnormal reactivity of the coronary arteries; data are being evaluated.